The present invention relates to a fan housing, particularly for a secondary fan of an internal combustion engine with a regulated three way catalytic converter.
This type of secondary air fan, which is predominantly multistage, is used in an internal combustion engine with a regulated three-way catalytic converter, to force air into the exhaust system and thus to initiate an afterburning of the exhaust gas.
In a known fan or blower housing of this type the disk-like housing cover is attached by self-tapping steel screws in a first housing part. These steel screws which are distributed uniformly circumferentially around the periphery of the first housing part extend over the entire axial length of the second housing part. Since particularly in a multistage blower the second housing part has a truly large axial length, the steel screws must be comparatively long threaded bolts. The second housing part is formed in two sections according to the structure of the multistage fan. Both housing part sections are connected aligned with each other. The connection of the second housing part sections to each other, the connection of the second housing part and the first housing part and of the second housing part to the cover occurs by a groove-projecting member joint in which projecting members and circular grooves engage each other in a positive locking manner.
This type of fan housing results in the generation of a comparatively large amount of noise during fan operation. Since the individual housing parts are made of plastic and the plastic has about a six times higher thermal expansion coefficient than the steel screws, a comparatively large tension results from the thermal expansion, which must be taken by the housing parts, so that they can be made only of a comparatively soft or yielding material.